The present invention relates to a method and an apparatus for detecting surface pattern unevenness generally by the use of a line sensor camera. More particularly, the invention relates to surface pattern unevenness detecting method and apparatus which permit effective use in the manufacture of a liquid crystal display panel (liquid crystal TFT substrate) or a polysilicon TFT substrate.
When manufacturing a liquid crystal display panel (liquid crystal TFT substrate), for example, it is necessary to apply a photolithographic process comprising the steps of exposing a substrate comprising a glass support, a metal (Cr) layer and a resist layer to a prescribed image by means of an exposure unit, and then, developing the thus exposed resist layer, thereby preparing a prescribed resist pattern.
At this point, a visual inspection is carried out by the use of a wide light source to check whether or not operation of the exposure unit is normal. One of the particularly important inspection items is the inspection of exposure unevenness on the resist layer caused by an abnormal focusing of the exposure unit. In the conventional art, it is difficult to automatically obtain an observation image of the resist pattern on the substrate surface. It is therefore the conventional practice to determine the extent of exposure unevenness by irradiating a monochromatic light source on the substrate and visually watching the reflected light from the resist edge of the resist pattern. According to this practice, however, the functional inspection by manual operation results in considerable dispersions, and further, the recent tendency of TFT substrates toward a larger size is making it difficult to carry out a visual inspection. There is therefore an increasing demand for automation of the exposure unevenness inspection.
Under the circumstances as described above, it is known to obtain an image on a substrate 1 which is a stationary object of inspection by means of a two-dimensional CCD sensor camera 10 as shown in FIG. 1. In this configuration, an image is obtained by means of the two-dimensional CCD sensor camera 10 arranged diagonally above an end of the substrate 1 by irradiating a light from a light source 20 from diagonally above the other end of the substrate 1 having a resist pattern on the surface thereof via a Fresnel lens 21 and a white scattering plate 22 onto the substrate 1.
However, because this configuration permits observation of exposure unevenness only within a tight angular range, while satisfactory observation is possible for the center portion of the substrate image 1G substantially corresponding to the center portion of the monitor 100, sufficient focusing is unavailable at top and bottom end portions. For a larger-sized substrate 1 to be inspected, therefore, it becomes impossible to observe unevenness throughout the entire surface of the substrate 1.
In order to obtain satisfactory focusing for the entire screen, a conceivable way is to include the image forming plane of a sensor camera 10 having a lens system 11 and a sensor 12 by an angle (.alpha.) in a direction in which the light receiving plane of the sensor 12 leaves the substrate 1 to be inspected, as shown in FIG. 2. This measure is not however acceptable because distortion at top and bottom of the screen of the monitor 100 becomes larger, as shown in FIG. 3.